Method of finishing gears



Oct. 14, 1952 W. S. PRAEG METHOD OF FINISHING GEARS Original Filed Nov. 8, 1948 2 SHEETS-SHEET l IN V EN TOR.

WALT .s, PRAA-G BY W M A from/16 Oct 14, 1952 w. s. PRAEG METHOD OF FINISHING GEARS IN V EN TOR.

2 SHEETS-SHEET 2 N m M? m 2 0 .m y wv 7 Original Filed Nov. 8, 1948 Alt-1 Patented Oct. 14, 1952 um'rso. STATES PATENT OFFICE METHOD OF FINISHING GEARS 1 Walter S. Praeg, Detroit, Mich., assignor to NationalBroach and Machine Company, Detroit,

' Mich., a corporation of Michigan Original application November 8, 1948, Serial No. 58,895. Divided and this application May 29,

1950, Serial No. 165,079

' 6 Claims. 1

The present invention relates to a method of finishing gears and more": particularly, to finishing gears by rotating them in mesh under pressure at crossed axes with a gear-like lapping tool.

The present application is a ,division of my prior copending' application, Serial No. 58,895 filed November 8, 1948, in which claims are directed to the machine for finishing gears.

It is an object of the present invention to finish gears by a method, characterized by the fact that it automatically. results in the removal of a predetermined amount of stock from the work gear independent of the actual size of the work gear prior to the finishing operation.

More specifically, it is an object of the present invention to provide a method of finishing gears in which a gear is meshed at crossed axes with a gear-dike finishing tool, preferably a, lapping tool, with the common ,:normal to the axis of the gear and tool spacedoutwardly from the adjacent end of the gearunder light pressure contact, thereafter rigidly maintaining the axis in spaced relatignship,.rotating thegear and tool in mesh, andeffectinga relative traverse between the gear-andtool in adirection efi'ective to distribute. the finishingtaction of the tool from end to end of the gearj teeth.

Other objectsandfeatures of the invention will become apparentas the description proceeds, especially when ken in conjunction with the accompanying :drawings, wherein:

Figure .1 is a front elevation of a gear lapping machine constructed irr accordance with the present invention., I

Figure 2-isa plan-view, partly insection, of the movable gear supporting table. v

Figure 3 is a section on the line 3-3 of Fig,- ure2. 1

Figure-A is a section on the line -4--4-of- Figure3. I

Figure 5 isa section'on the line 55 of-Figure 2.- p v Figure 6 is an,enlarged; sectional view of parts shown in Figure 3. I

Figure 7 is an enlarged diagrammatic view of a rotary cam. I z

Figure 8 is a, fragmentary section showing a detail of the machine The herein disclosed method may be carried out by widely different mechanisms but a machine for carrying out the herein disclosed meth- 0:1 is illustrated in rthedrawings.

Referring first, to Figure 1, .the' gear lapping machine comprises I a pedestal I0 provided with a forwardly projecting overhanging portion." I I,

2 i to the underside of which is mounted a lapsupporting head I2. The lap supporting head I2 is mounted for angular adjustment about; a vertical axis to permit variation in the crossed axes angle between the gear and lap. A motor (not shown) is mounted in the portion H of the machine and is adapted to rotate the lap supporting spindle I3 through suitable mechanism. Mounted for vertical adjustment on ways provided at the front of the pedestal I0 is a knee I5 having horizontal ways extending transversely of the machine. Mounted on these ways for back and forth reciprocation is a carriage 20. Located within the base of the machine is a, motor which includes drive means for effecting relatively slow reciprocation of the carriage 20 and control means for the motor are provided including suitable switches having switch actu ators 22 and 24 adapted to be engaged by adjustable dogs 26 and 28. Mounted on the carriage 20 is a rocking subtable 30, a suitable trunnion connection indicated at 32 being provided between the carriage 20 and the subtable 30. The stationary bas'efof the machine includes an adjustable cam indicated generally at 34 and a cam follower 35 is mounted on a rocking table. Releasable clamping means 36 and 38 are provided for locking the sub-table 30 in intermediate position when it is not desired to employ the cam for rocking the platform. The upper surface of the table terminates in a circular plate 40 provided with circular T-slots (not shown) on which is mounted an angularly adjustable table 42 Whichmay be angularly adjusted about a vertical axis. The table ,42 has a platform 50 connected thereto for relative movement toward and away fromthe head I2 and the platform 50 is also provided. with adjustable slots 52 for supporting head and tailstocks '53 and 54which include centers between which is mounted a work gear W. I

In the operation of the machine a work gear ,W'is mounted between the head and-tailstocks means are provided for biasing the platform 5| toward the head I2 with a substantially, constant but relatively small force. When the teeth of the gear W and the lap L have come into light pressure contact as a result of the biasing force aforesaid, the platform 50 is rigidly locked in position, after which the gear lapping operation takes place. 'The gear lapping operation results from relatively rapid rotation of the gear and lap in mesh and reciprocation of the carriage 20. During this operation the table 42 is in angularly adjusted position so that the axis of the work gear W extends at an oblique angle with respect to the direction of traverse of the carriage 20. Furthermore, the head I2 is angularly adjusted so that the lap will mesh with the work gear W with the axes of the gear and lap crossed at a limited angle as between three degrees and twenty degrees.

In order to effect engagement between the teeth of the gear and lap under light but substantially constant pressure contact as aforesaid, the detailed construction illustrated in Referring first to Figures 2-6 is employed. Figure 3, the platform 59 is pivoted to the table 42 by a pivot pin 60. Adjacent the forward edge of the platform 50 are adjustable biasing springs 6!, best seen in Figure 5, these springs seating at their lower end against the table 42-, which as. previously noted. is clamped .in. angularly adjusted position on the rocking table 30, suitable clamping bolts being shown at 62'. A cup-shape adjusting plug 63 is threaded into a threaded opening as shown- By. means of, the construction, a substantially .constant'biasing force is provided which may be adjusted so as to urge the platform. upwardly so as to cause contact between. the gear and lap to take place under uniform light pressure conditions, independent of the actual position of the platform whencontact is established. v

vMeans. are provided for rigidly locking, the

platform in adjusted position. These means are for the most part located in a housing Gtdoweled and bolted to the forwardly extending free edge of the platform 5.0. This housing, includes a recess 65 (Figure 6) which receives an inverted U-shaped yoke 66 secured by bolts 61 (Figured) to the table 42. Beneath the yoke 66 is a hardened wear plate. 68.

Extending forwardly from the platform 50 is acamming and clamping structure which is permitted limited upanddown movement between the yoke '66 and plate 68.

This structure comprises anelongated threaded stud "l rigidly and non-rotatably mounted in the forward edge of the platform 50. 'Rigidly seated in a recess in the forward edge of the platform 50 is a wedging element 12, which as illustrated may be held in placeby stud I0. Element 12 has upper and lower inclined surfaces 73 and 14 respectively. Threaded .to the stud 1.0 for rotationand longitudinal motion thereon isa nut 15, having pinion. teeth [6, a cam 11 andl a cylindrical or spherical end portion lB. A carrier plate 80, havinga spherical seat therein interfitting with the sphericalfend portion J8. of .the nut, is received between the nut and wedge element 12, and is provided with an enlarged bore 8| so that it may rock on its spherical seat.

Plated!) has pairs of forwardly projecting ears 82 carrying pins 83 on which rollers 84 are mounted. The. rollers 84 have substantial clearance with respect to pins 83', as illustrated, and .are thereforeradially movable thereon.

' Cam 11, 'as best seen in Figure '7, has a high portion of uniform radius between radii R2, a

low portion of uniform radius. between radii RI,

and rise and fall portionsbetween radii RI and R2. Bias spring 6| keeps the platform elevated to'keep cam 11 in contact with the underside of yoke 66 except when the teeth of the gear and lap depress the platform. When the high portion of the cam between radii R2 is in contact with the yoke, the platform is depressed to loading position.

Referring again to Figure 2, an air cylinder 90 is supported by the housing 64 and is provided with a piston connected to a piston rod 9| which is threaded or otherwise suitably secured to an actuating bar 92 which is provided with rack teeth 93 at its underside which mesh with the pinion teeth 16 formed on the nut 15.

With the cam 11 in position such that the raisedportion thereof intermediate the radii R2 is in contact with the underside of the cross piece of the yoke 66, the platform 50 is in depressed or loading position. At this time a work gear W maybe mounted between head and tailstocks 53, 54 and it will be in loose mesh with respect to'the lap L. -At this time the apparatus is in condition for initiation of an'automatic cycle. This cycle comprises initially admitting motive fluid to the cylinder 90 which will cause the bar $2 to..move to. the right as seen in Figure 2, thereby rotating the nut I5. Initial rotation of the nut will cause corresponding rotation of the cam ll formed thereon and will move the elevated portion of the cam between radii R2 out of engagement with the yoke 66 and will thus permit upward locking movement of the platform'50 under the biasing force supplied by the compression springs 6|. Upward movement of the platform 50 continues until the teeth of the work gear W and lap L come into light pressure contact, this contact being established by the adjustment of the compression springs 6|. The position of theplatform 50'when its upward motion is thus arrested will depend upon the exact dimensions of the work gear and thus may vary between small limits.

,It, is essential in order that the subsequent lapping operation-be carried out under suitable conditions for the platform to be rigidly locked in position during the traverse strokes.

' Rotation of the nut 15, in addition to moving the cam 17 as just described, also advances the nut 15 to the'right, as seen in Figures 3 and 6. Preferably the threads provided between the stud 10 andthe nut :15 have a substantial lead so that rotation of thenut in-an amount between degrees and 225 degrees will effect locking of the platform. Locking of the platform is effected by causing-the rollers to be interposed in wedging or abutting relation between three angularly disposed surfaces. These surfaces are the upper and lower inclined surfaces 13 and 14 of the wedge member, the lower surface of the yoke 66, the upper-,surface'of the wear plate 68, and the end surfaces of the-carrier plate 80. If it so happens that the platform and hence the stud 10 is in intermediate position with respect to the yoke and wear plate, the rollers 84 will enter into looking engagement as described without rocking of the carrier plate on its spherical or cylindrical seat. If, however, the stud l0 and associated mechanism is closer to either the underside of ried by a single rigid carrier plate 80, it will be pp re t that when the nut 1.51s advanced to the rigid elements between relatively movablesun,

faces.

Since rotation of by an air cylinder, forward movement, of the pis-' ton in the cylinder willbe arrested when the roll-. ers 84 come into engagement with the lockingsurfaces. Preferably automaticcontrols are provided for thereafter initiating rotation of the lap and traverse of the carriage 20. The first stroke of traverse is arrested by operation of reversing switches having actuators such as ,22 or 24 which initiate a return stroke of traverse. Upon completion of the return stroke of traverse, rotation of the lap and gear is stopped and the motive fluid is admitted to thecylinder. so. as to cause reverse movement of the pistontherein. {This will move the rollers 84 out of locking-engage-v ment and will also rotate. the cam :l-T; so. as to bring the elevated portion thereof into engagement with the underside of the yoke element. This has the result of moving the platformifl downwardly so as to bring the lap and work gear into loose mesh, at which time the completed work piece may be removed. The present'machine is designed to carry out a lapping opera! tion which is characterized by its short cycle and by the fact that it is intended to remove a substantially uniform amount of material from the teeth of a series of work gearsindependent of small Variations in size between such work gears.

As previously stated, the operation is intended to be carried out with the axis of the work gear W inclined to the direction of traverse of the carriage 20. This has two important results which make possible the present operation. In th first place, by properly selecting the .angularity between the axis of the work piece and the direction of traverse, it is possible to cause the finishing action between the lap andWOrk piece to be distributed substantially from end to end of the teeth of the lap. This has the effect of, greatly increasing lap life and preventingl-ocalized wear on the lap teeth. At the same time it results in a more efiicient lapping action which removes the requisite amount of material from theteeth of the gear without the necessity of repeated reciprocations, as has been required in prior lapping methods.v V

A third result of the use of traverse in a direction diagonal to the axis of the work gear is the gauging of the amount of material to'be removed from the teeth of the work gear by the simple expedient of locating the work gear in a definite position relative to traverse when it is moved upwardly into mesh with the teeth of the lap. If the position of the work gear issuch that the common normal to the axes oi the'lap andgear lies outside of the edges of the work'gear, subsequent traverse will bring theteeth of the lap full} amount per-.

the nut element. iseflected,

geisha it is particularly. pointed out thatlthe present method is not intended primarily for accurate control of final dimensions of the gear, since the final position of the work, supporting'platform present method is intended as a production step. in the mas-s production of gears and ,contemplates that the lapping will be appliedto all gears for the purpose 'ofimpro-vin surface finishing and effecting correction o-f'suchJgear characteristics as profile, lead, concentricity, etc. Tests in production have shown that the present method improvesthe operatingicharacteristics of gears by a very considerable factor and since itispossible to carry out this operation ata; highproduction rate, it makes production lapping. a practical operation in the mass production of gears. The foregoing description has'been made with particular reference to :useof the machine as-a gear lapping machine. However, it will-be readily appreciatedthat-the inventionmay be practiced when gear finishing toolsof different type are employed. .Thus, for example, the machine ,may be used with a gear'shaving tool in which the teeth ofthe gear-like tool are provided I H with parallel serrations, forming adjacent cutting and gear into mesh at a center distance which requiring the careful attention: of theioperator. I

It is necessary only for the operator to remove and replace work gears between the head and tailstocks, the remainder of the operation being fully automatic.

edges and guiding lands. The principal difference between lapping andshaving resides in the fact that the gear shaving operation. iS' flIl accurate cutting operation in which a definite amount of stock may be removed-in a'single traverse of the gear and tool, whereas in lapping the material of the gear teeth is-worn away by a rubbing action. I r 1 The machine as illustrated in Figure 1 is ordinarily provided with mechanism for effecting vertical adjustment of the-kneel5 and the prior practice has been to provide a plurality of reciprocations, at the end-of each of which the knee maybe fed upwardly'by a'small predetermined amount so as to *take'a cut. of corresponding amount on the teeth of the gear on the next stroke of traverse. The: present invention may be combined with the. machine including the. vertical feed of. the knee; so as to carry out a new and improved method-of finishing. Thus, for example, the gear and tool maybe brought into light pressure contact as previously described, after which the first stroke of traverse may be taken. Upon completion of thefirst stroke of traverse and before initiation of the return stroke, the knee-may be fed upwardly by a small predetermined amount. ,This method may if desired include additional strokes of traverse, although it is contemplated ordinarily. that the gear will be completely finished in two strokes of traverse or a single back and forth reciprocation of the parts.

:-.The machine is-further capable of carrying out another modified method in which the air cylinder is actuated at-the end of the first stroke of traverse sothat the platform. 50 may move upwardly to a new position so asto remove a definite amount of stock on the return stroke.-

moval of stock upon each stroke of traverse either by shaving or lapplngand the final dimension of thegear may be determined by providing an independent abutment which limits upward movement of the platform '50. I

Preferably suitable means are provided for initially positioning the platform 50 in a prede termined intermediate position during setup of the machine for a run of gears. This means may constitute merely witness marks brought into desired. The initial setup will then involve depressing platform 50, rotating bolt 99 to bring projection I beneath lug 98, releasing platform 50 to permit it to rise to the intermediate position determined by engagement between lug 98 and projection I00, loading a work gear between the stops 53 and 54, and. vertical adjustment of the knee l to bring the gear and tool into mesh and preferably into light contact. Thereafter if an oversize gear is inserted the platform 50 may be depressed to a position below the initial set position as determined by the locating means, and if an undersize gear is present the platform will come to rest in a position above the position determined by the locating means. If a carefully checked or master gear is used in the initial setup it will insure that the average position of the platform during the first shaving stroke of traverse will be the predetermined intermediate position as set by the locating means. The upper surface of projection I00 may if desired be an inclined camming surface so that different rotational position of bolt 99 will predetermine different positions in which platform 50 is locked during initial setup.

The drawings and the foregoing specification constitute a description of the improved method of finishing gears in such full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of which is indicated by the appended claims.

What I claim as my invention is:

l. The method of finishing lapping a series of gears which comprises'sequentially meshing the gears at crossed axes with a gear-like lapping tool under a relatively small, uniform pressure, with the common normal to the axes of gears and tool spaced outwardly beyond the ends of the gears more closely adjacent to said common normal to thereby determine the amount of stock to be removed from the gears, locking the gears and lap in the position of radial spacing determined by their meshed engagement without reference to the theoretical dimensions of the ears, and effecting relative traverse between the gears and lap in a direction to distribute the lapping action longitudinally of the gear teeth while rotating the gear and lap. a

2. The method as defined in claim 1 in which the relative direction of traverse is diagonal to the axes of both lap and gears.

3. The method of finishing a gear which comprises initially meshing a gear member with a gear-like tool member with the axes of said members crossed at an angle of less than 30 degrees and with the common normal to the axes of said members lying a predetermined distance beyond the side of one of said members, thereafter effecting a relative radial movement between said members to bring the teeth of said members into contact with a predetermined relatively light pressure, thereafter effecting rigid locking of the members to maintain the spacing between the axes thereof, and rotating said members and effecting relative traverse between said members in a direction to cause the common normal to the axes of said members to pass from one side of said gear member to the other side thereof.

4. The method of finishing gears as defined in claim 3 in which the relative traverse between the gear and tool members is continued until the common normal to the axes of said members lies a predetermined distance beyond the other side of said one member, thereafter unlocking said members and effecting relative radial feed between said members to bring the teeth of said members into contact with the same predetermined relatively light pressure, thereafter effecting rigid locking of the members to maintain the spacing between the axes thereof, and finally effecting a reverse stroke of traverse.

5. The method of finishing gears as defined in claim 3 in which the relative traverse between the gear and tool members is interrupted when the common normal to the axes of said members is located a predetermined distance beyond one side of said one member, thereafter arresting said relative traverse, unlocking said-members, effecting a relative radial feed between said members to bring the teeth of said members into contact with the same predetermined relatively light pressure, thereafter effecting rigid locking of the members to maintain the spacing between the axes thereof, and finally effecting further relative traverse between said members.

6. The method of lapping a gear hich comprises supportingthe gear for rotation on a vertically movable support, 'counterbalancing the weight of the support with a uniform force providing a relatively small substantially constant force effective to raise said support, limiting upward movement of said support by engagement between a gear on said support and a stationary gear-like lap, locking said support in the position determined by meshing engagement between the gear and lap, and thereafter rotating and traversing said gear and lap in mesh.

WALTER S. PRAEG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,989,651 Drummond Jan. 29, 1935 2,114,616 Sykes Apr. 19, 1938 2,582,408 Bauer Jan. 15, 1952 FOREIGN PATENTS Number Country Date 834,409 France Aug. 16, 1938 

